1. Field of the Invention
This invention relates to a method and apparatus for applying forces to glass being formed into a continuous sheet of glass while floating on molten metal. More particularly the invention relates to method and apparatus for more efficient regulation of forces to either spread the glass to a thinner than equilibrium condition or prevent the glass from becoming as thin as in equilibrium conditions.
2. Description of the Prior Art
The following U.S. Patents describe the devices and methods for regulating the thickness of a layer of glass floating on a molten metal bath to achieve a thickness other than equilibrium.
U.S. Pat. No. 3,695,859 to Dickinson et al discloses a method of float glass formation wherein several pairs of tractive rollers are applied to the top surface of float glass to control the width of the glass during attenuation.
U.S. Pat. No. 3,661,548 to Ito et al discloses the application of a series of toothed wheels in freely rotating contact with a floating glass ribbon. The wheels are angled outwardly in order to widen the floating glass ribbon beyond equilibrium width.
U.S. Pat. No. 3,684,471 to Matsushita discloses the application of a series of driven wheels to a molten glass ribbon to cause it to have a width wider than equilibrium. The rollers or wheels are electrically conductive and are used to heat the ribbon in order to aid in the widening of the ribbon.
Greenler et al, U.S. Pat. No. 3,520,672, discloses a method wherein a series of driven knurled rolls are applied to a glass ribbon in order to attenuate it beyond equilibrium thickness.
U.S. Pat. No. 3,929,444 to May et al, discloses a process wherein edge rollers such as in the above patents are applied from an overhead rail in order to eliminate crowding caused by the conventional application of the rollers to the glass ribbon floating on molten metal.
U.S. Pat. No. 3,713,797 to J. Lawrenson discloses apparatus wherein a rotary member having a vertical axis is utilized to laterally stretch a molten glass ribbon by engaging the ribbon margins with the edge of the rotary member and impelling it outwardly.
The above processes suffer from the disadvantage that their efficiency is low requiring several systems of rollers. This leads to cluttering of the area around the furnace with these controls and further requires a complicated regulation system to change the angle, speed and pressure of these rollers in order to regulate the thickness of the glass being formed. The construction and maintenance of several banks of rollers requiring cooling and regulation means is expensive and limits the amount of other controls which may be allowed access to the furnace. Further, several of these mechanisms such as the Lawrenson U.S. Pat. No. 3,713,797 apparatus, require careful regulation of the area of contact between the edge of the glass sheet and the roller. This is not easily regulated when the location of the edge of the ribbon changes in response to other process factors.